It is known to provide data processing devices with additional circuitry for enabling the data processing device to test its own integrity. Such a test is known as a built in self test (BIST). A data processing device may be arranged to perform a BIST a limited number of times, e.g., prior to handing the data processing device over to a customer, or repeatedly, e.g., many times during the entire life time of the data processing device. A data processing device that is operated for safety critical applications, e.g., in a motorized vehicle such as a car or truck, may be required to perform a BIST repeatedly at prescribed intervals. For example, a BIST may be performed immediately after powering on the device and then once every twelve hours, for example. When the device is carrying out a BIST, the functionality of the device may be reduced. The duration of the interval between two subsequent BISTs may therefore be a compromise between the desire of monitoring the integrity of the device and the desire to maximise the time during which the device is fully operational.
A data processing device may comprise data storage circuitry and data processing circuitry. A test of the data storage circuitry performed by the data processing device is known as a memory built in self test (MBIST). A test of the processing circuitry performed by the data processing device is known as a logic built in self test (LBIST). An LBIST may affect the functionality of the data processing device more severely than an MBIST. In fact, when running an LBIST, the processing circuitry may be unavailable for any other purpose.